The present invention relates to a measuring system for detecting a rotary-linear displacement of a shaft comprising a linear sensor and a rotary sensor. In particular, the present invention relates to a rotary-linear drive which is equipped with such a measuring system.
A drive, particularly an injector and metering unit in a plastic injection molding machine or similar machine applications requires the implementation of a rotary displacement and a linear displacement on the drive shaft. It must be possible to generate these displacements independently of one another, on the one hand, but also superimposed. Control of the combined drive requires implementation of a rotary and linear positional measurement with the aid of a measuring system.
Hitherto, rotary-linear drives were available which have, for example, the structure reproduced in FIG. 1. The drive consists of a rotary drive 1 and a linear drive 2 which are arranged axially behind one another and linearly and rotationally move a common shaft 3. The combined displacement is measured or detected with two sensors 4 and 5. The rotary sensor 4 detects an angular position of the magnetic field of magnets 6 which are arranged in a hollow shaft 7 which is permanently connected to the shaft 3. The linear sensor 5 in a tube section 8 which protrudes into the hollow shaft 7 and at which the rotary sensor 4 is mounted registers changes in inductance which are caused by magnets 9 which are arranged at the hollow shaft 7.
The rotary sensor 4 and the linear sensor 5 are in each case invariant with respect to the displacement which is not to be measured. However, the accuracy of this measuring system is not suitable for all applications.